[unreadable] This research will be done primarily in Slovakia as a FIRCA supplement to NIH grant # P01 CA82267 (Project 4). Breast cancer is the most commonly diagnosed cancer in women in SIovakia, and the leading cause of death. There are emerging data that fetal, early childhood and adolescent exposures related to growth, body mass and physical activity may be associated with the risk of breast cancer. We propose to evaluate these questions in a hospital-based case-control study in western Slovakia. Cases (N=250) will be women aged 20-70 years who are first diagnosed with invasive breast cancer from 1/1/2003 through 6/30/2005 and are residents of Trnava or Senica districts at the time of diagnosis. Cases will be rapidly ascertained through surveillance of the district hospitals in Trnava and Senica. Controls (N=250) will be women with no history of breast cancer, aged 20-70 years, and who are residents of Trnava or Senica district. Controls will be frequency matched to cases by age group and district, and will be randomly selected from the primary care medical practices in each district. Participants will complete a standardized in-person interview and provide a blood sample. Through interviews and abstraction of medical/population records, we will collect data on fetal exposures (birthweight, birth length, gestational age, twinning/zygosity, pre-eclampsia, etc.), childhood anthropometrics (height and weight at various ages), and adolescent exposures (anthropometrics, age at menarche). We will also collect data on other key breast cancer risk factors, including reproductive and adult anthropometric variables, in order to evaluate confounding. Genomic DNA will also be collected from peripheral blood, and banked in order to conduct future studies on the role of common genetic polymorphisms in candidate genes, as well as gene-environment interactions, in the etiology of breast cancer. There is sufficient statistical power to test the a priori hypotheses of interest. We have assembled an international research team for this study. This study will address an important scientific question in breast cancer etiology, and these data would be expected to better inform the primary prevention of the disease. This study will also develop infrastructure and experience in Slovakia for the conduct of cancer epidemiology studies, and generate the necessary preliminary data for expansion of this research effort. [unreadable] [unreadable]